Light-welterweight Tom Stalker is the sixth British male boxer through to the Olympic quarter-finals after beating India's Manoj Kumar in his opening bout.
Stalker, who received a first-round bye, showed signs of ring rust in a torrid encounter.
After a fast start, the GB team captain tired alarmingly but held on to
clinch the decision 20-16.
Team GB's male boxers into the last eight
- Andrew Selby
- Luke Campbell
- Tom Stalker
- Fred Evans
- Anthony Ogogo
- Anthony Joshua
Belfast's Paddy Barnes reached the last eight
of the light-flyweight contest.
Stalker, 28, beat Kumar in the quarter-finals of last year's World Championships.
And the Liverpudlian, obviously fired up having spent the last week on the sidelines, came charging out of the blocks, taking the first round 7-4.
However, the second round could have gone either way, with Stalker playing into Kumar's hands and the Indian having plenty of success from close range.
But Stalker carried a seven-point lead into the final round and, although he looked very weary indeed when the final bell sounded, he held on for the win.
Barnes is pleased with his display in beating Essomba
"I can improve a lot," he said. "I felt like I was staying there and fighting too much, rather than hitting and moving. My next bout I'll be a lot better. If I want to win the gold medal there's got to be a lot more to come.
"After having over a week in the village I didn't feel 100% sharp. But the fans got me through it - I'd like to thank every single one of them for such amazing support."
Stalker will fight Mongolia's Munkh-Erdene Uranchimeg for a medal after the world number two saw off Richarno Colin of Mauritius 15-12.
On the opposite side of the draw to Stalker, Brazilian world champion Everton dos Santos Lopes was beaten by Beijing bronze medallist Roniel Iglesias Sotolongo of Cuba 18-15.
Barnes, a bronze medallist in Beijing, picked off Thomas Essomba to secure a comfortable 15-10 win, before tweeting news of his victory from the ring.
The 25-year-old said:
"Job done from the Olympic ring. Paddy Barnes - bringing you closer to the action." He later added: "Think I'm the first boxer to tweet from inside [the] ring."
Next up for Barnes, who is the third Irishman into the quarter-finals, is India's Devendro Singh Laishram, who beat fourth seed Serdamba Purevdorj 16-11.
The man who beat Barnes in Beijing, China's three-time world champion Zou Shiming, beat Yosbany Veitia Soto of Cuba 14-11.